A whole prime rib roast has 7 bones and weighs about 17 to 20 lbs. Butchers often divide the whole roast into two parts: 3-bone roast from the small end and 4-bone roast from the larger diameter end for serving size that's more manageable for most customers. Costco sells them this way as well as whole roasts. I'd recommend against anything smaller than a 3-bone roast (weighs about 6 lbs.).

FYI...re: Costco ...I found out something today...the cut based on a price minimum so in Prime grade they had several 2 bone roasts as they are priced high enough to meet their minimum. In Choice they cut only 3 or 4 bone.

Thanks, that's good to know. I cooked a 3-bone prime grade roast from Costco for Christmas dinner. i dry aged it for 8 days in the fridge, wish I'd had time to keep it longer.

And, I'll explain the reason for recommending against a 2-bone roast. This came from the old-fashioned butcher in my home town. He will cut any size the customer wants but when I asked for 2-bone he tried to talk me out of it. The reason is the sad stories he hears from customers who mess up with the smaller roasts. One needs to be more careful in cooking the smaller size, keep a closer eye on the temperatures with a good meat thermometer, and know how to adjust the recommended cooking times as most instructions are for a different surface:volume ratio. I have done 2-bone roasts myself, as have others in this thread, but add that caution if one is less experienced or has less cooking savvy. The various threads on the Home Cooking board attest to the angst that many have over making a prime rib, and while some can't relate, that's the reality for most people.

FWIW I reckon that the meat from the smaller end of the cut is rather better to eat. Also, I've had success with a 1 bone cut for two people (about 2lbs.) by searing in a hot pan for about 3 minutes per side and finishing in the oven at 400 for about 15 minutes, rested for a further 5 mins.

Really? Maybe I'm mistaken then? I thought the smaller end, being towards the rear, was closer to what we in the UK call the sirloin, and therefore superior. Does anyone know if there's any real variation along the ribs?

You very well could be right. Looking at the photo in the link it would appear the smaller ribs are closer to the middle of the cow (furthest from the hoof). I may need to have a talk with my butcher who talked me out of getting the small end!

We recently had a very tough rib roast that I bought at a great market in Sonoma, CA. Tough to the point that I actually took it back to the store. They were SO nice about it and made no excuses. But he did say to always specifically ask for the small end because it's more tender.

I totally agree that a smaller roast is much more likely to be overcooked. I offered that in case anyone really wanted a smaller roast but all your info will no doubt help many who have cooked few if any standing rib roasts. What is the longest you've dry aged it in the fridge? I'm always trying longer and longer.

I recently dry aged a 9 pound boneless ribeye roast for 24 days. The caveat is that I'm lucky to have a second refrigerator that can go days without being opened (primary purpose is to store milk, OJ, eggs and other stuff acquired in bulk), which is where I dry aged this toast. I wouldn't dare try to dry age in my primary fridge, as the repeated opening and closing of the doors means the humidity level is too high for me to feel secure about the aging process.

I know someone who has his butcher dry age for 42 days. That's really pushing it IMO.

As for my result, it was a very beefy taste with a firmer, less "waterlogged" texture to the beef. I'm a fan and will certainly do this again whenever the occasion and company allows for it. I'll probably go out to the 30 day mark next time.

I'd be shocked if you couldn't get one at Whole Foods. I was at Whole Foods in Oakland on Christmas Eve and they still had plenty, so I'm sure they'll have them if you want one for New Years. Call them and check, but you should be good.

My Safeway had a large selection (Ocean Beach) two days ago but I would presume most of them would have it, and would probably cut cut it for you. It was on holiday sale, so I think they should have them through New Year's.

I usually take the reference to prime rib to refer to a standing rib roast, regardless of grade of meat. From the OP's latest response, it sounds like he did want a prime grade rib roast though - sorry to lead anyone astray.